Electrode binder polymer, electrode binder, electrode binder composition, electrode slurry, electrode, secondary battery, production method for electrode binder polymer, production method for electrode binder, production method for electrode binder composition, production method for electrode slurry, and production method for electrode

Abstract

An electrode binder polymer according to the present invention has a first functional group, which is at least one moiety selected from the group consisting of a carboxy group and a carboxy group forming a salt, and a second functional group, which is at least one moiety selected from the group consisting of an isocyanato group and a blocked isocyanato group, said electrode binder polymer having a glass transition temperature Tg of -3°C or higher.

Description

Electrode binder polymer, electrode binder, electrode binder composition, electrode slurry, electrode, secondary battery, method for producing electrode binder polymer, method for producing electrode binder, method for producing electrode binder composition, method for producing electrode slurry, and method for producing electrode

[0001] The present disclosure relates to an electrode binder polymer, an electrode binder, an electrode binder composition, an electrode slurry, an electrode, a secondary battery, a method for producing an electrode binder polymer, a method for producing an electrode binder, a method for producing an electrode binder composition, a method for producing an electrode slurry, and a method for producing an electrode.

[0002] Because secondary batteries can be made smaller and lighter, they are widely used as power sources for notebook computers, mobile phones, power tools, electronic communication devices, etc. In recent years, secondary batteries have also been used as power sources for electric vehicles, hybrid vehicles, etc. A typical example of a secondary battery is a lithium-ion secondary battery.

[0003] A secondary battery includes a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolyte. The positive electrode and negative electrode each include a current collector and an electrode active material layer formed on the current collector. The electrode active material layer typically contains a binder, which binds the active materials together and the active materials to the current collector. Examples of binders used in secondary batteries include those described in Patent Document 1 and Patent Document 2.

[0004] Patent Document 1 describes a secondary battery electrode having an electrode layer containing 100 parts by mass of at least one polymer selected from the group consisting of styrene-butadiene copolymers and copolymers obtained from a (meth)acrylic acid ester and a vinyl monomer having an acid component, and 1 to 20 parts by mass of at least one nonionic surfactant having a cloud point of 70°C or lower and selected from the group consisting of polyoxyethylene alkyl ether derivatives, polyoxyethylene-polyoxypropylene condensates, and polyoxyethylene-polyoxypropylene alkyl ether derivatives.

[0005] Patent Document 2 describes a binder for lithium ion secondary battery electrodes, which has a glass transition temperature of 30°C or lower and is obtained by emulsion polymerization of ethylenically unsaturated monomers containing, as essential components, 15 to 70% by mass of styrene relative to the total amount of ethylenically unsaturated monomers, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, and an internal crosslinking agent in the presence of a surfactant.

[0006] Furthermore, Patent Document 3 describes an electrode binder containing a polymer having a constituent unit derived from a (meth)acrylic acid alkyl ester monomer, a constituent unit derived from a monomer with a specific structure having an aromatic group, and a constituent unit derived from a monomer having at least one group selected from the group consisting of an epoxy group, a (blocked) isocyanate group, and a urethane group.

[0007] JP 2014-239070 A JP 2011-243464 A WO 2023 / 053863

[0008] In recent years, secondary batteries are required to maintain sufficient battery performance even when exposed to a high-temperature environment for a long period of time, that is, to have excellent high-temperature storage properties.

[0009] Therefore, an object of the present disclosure is to provide an electrode binder polymer, an electrode binder, an electrode binder composition, an electrode slurry, and an electrode that can provide a secondary battery with excellent high-temperature storage stability. Another object of the present disclosure is to provide a secondary battery with excellent high-temperature storage stability. Another object of the present disclosure is to provide methods for manufacturing the electrode binder polymer, the electrode binder, the electrode binder composition, the electrode slurry, and the electrode.

[0010] The present disclosure includes the following aspects. <1> An electrode binder polymer having a first functional group which is at least one type selected from the group consisting of a carboxy group and a carboxy group which forms a salt, and a second functional group which is at least one type selected from the group consisting of an isocyanato group and a blocked isocyanato group, and having a glass transition temperature Tg of -3°C or higher. <2> The electrode binder polymer according to <1>, having a glass transition temperature Tg of 50°C or lower. <3> The electrode binder polymer according to <1> or <2>, wherein the content F1 of the first functional group is 0.20 mmol / g to 5.0 mmol / g. <4> The electrode binder polymer according to any one of <1> to <3>, wherein the content F2 of the second functional group is 0.020 mmol / g to 2.0 mmol / g. <5> The electrode binder polymer according to any one of <1> to <4>, wherein the ratio F2 / F1 of the content F2 of the second functional group to the content F1 of the first functional group is 0.020 to 2.0. <6> The electrode binder polymer according to any one of <1> to <5>, which has dispersibility in water. <7> An electrode binder comprising the electrode binder polymer according to any one of <1> to <6>. <8> An electrode binder composition comprising the electrode binder polymer according to any one of <1> to <6> and an aqueous medium. <9> An electrode slurry comprising the electrode binder polymer according to any one of <1> to <6>, an aqueous medium, and an electrode active material. <10> An electrode comprising a current collector and an electrode active material layer comprising an electrode active material and the electrode binder polymer according to any one of <1> to <6>. <11> A secondary battery comprising the electrode according to <10>. <12> A method for producing the electrode binder polymer according to any one of <1> to <6>, comprising copolymerizing a compound having the first functional group and an ethylenically unsaturated bond with a compound having the second functional group and an ethylenically unsaturated bond. <13> A method for producing an electrode binder, comprising mixing the electrode binder polymer according to any one of <1> to <6>. <14> A method for producing an electrode binder composition, comprising mixing the electrode binder polymer according to any one of <1> to <6> with an aqueous medium, or mixing the electrode binder according to <7> with an aqueous medium.<15> A method for producing an electrode slurry, comprising mixing the electrode binder polymer according to any one of <1> to <6>, an electrode active material, and an aqueous medium, mixing the electrode binder according to <7>, an electrode active material, and an aqueous medium, or mixing the electrode binder composition according to <8> and an electrode active material. <16> A method for producing an electrode, comprising applying the electrode slurry according to <9> to at least a part of a surface of a current collector and drying the applied electrode slurry.

[0011] According to the present disclosure, it is possible to provide an electrode binder polymer, an electrode binder, an electrode binder composition, an electrode slurry, and an electrode that can obtain a secondary battery with excellent high-temperature storage properties. Furthermore, according to the present disclosure, it is possible to provide a secondary battery with excellent high-temperature storage properties. Furthermore, according to the present disclosure, it is possible to provide methods for manufacturing the electrode binder polymer, the electrode binder, the electrode binder composition, the electrode slurry, and the electrode.

[0012] The following describes the embodiments in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0013] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. A numerical range "A or greater" means A and a range exceeding A. A numerical range "A or less" means A and a range less than A. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0014] In the present disclosure, unless otherwise specified, each component may contain multiple types of corresponding substances. When multiple types of substances corresponding to each component are present in a composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition, unless otherwise specified.

[0015] In the present disclosure, the term "layer" includes cases where the layer is formed over the entire area when the area in which the layer exists is observed, as well as cases where the layer is formed over only a portion of the area.

[0016] In this disclosure, "(meth)acrylic" is a general term for acrylic and methacrylic. "(meth)acrylate" is a general term for acrylate and methacrylate. In this disclosure, "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability, unless otherwise specified.

[0017] <Electrode Binder Polymer> The electrode binder polymer of the present disclosure has a first functional group which is at least one type selected from the group consisting of a carboxy group and a carboxy group that forms a salt, and a second functional group which is at least one type selected from the group consisting of an isocyanato group and a blocked isocyanato group, and has a glass transition temperature Tg of −3° C. or higher.

[0018] Use of an electrode binder polymer having the above-described configuration makes it possible to obtain a secondary battery with excellent high-temperature storage properties. The reason for this is unclear, but can be speculated as follows. It is believed that the isocyanato group present as a second functional group in the electrode binder polymer, or in the case of a blocked isocyanato group, the isocyanato group generated by heating, voltage application, chemical reaction, etc., generates active species through an oxidation-reduction reaction during charging and discharging at the electrode. It is believed that this active species reacts with at least one of the electrolyte solution and the coating (SEI, Solid Electrolyte Interphase) generated on the surface of the electrode active material by oxidation-reduction of the electrolyte solution, thereby allowing the electrode binder polymer to strongly protect the surface of the electrode active material. The surface of the electrode active material strongly protected by the electrode binder polymer has excellent durability at high temperatures such as 60°C. It is believed that this suppresses undesired decomposition reactions of the electrolyte solution and electrolyte that occur on the surface of the electrode active material during high-temperature storage, thereby improving high-temperature storage properties.

[0019] Furthermore, it is believed that the carboxyl groups present as first functional groups in the electrode binder polymer and the carboxyl groups that form salts improve adhesion to the current collector, thereby improving high-temperature storage characteristics. Furthermore, when the glass transition point of the electrode binder polymer is −3° C. or higher, the film rupture strength of the electrode binder polymer is improved, and this, together with the presence of the first functional group and the second functional group in the electrode binder polymer, synergistically suppresses an increase in electrode resistance after placing an electrode containing the electrode binder polymer in a high-temperature environment.

[0020] The first functional group content F1 of the electrode binder polymer of the present disclosure is preferably 0.20 mmol / g or more, more preferably 0.50 mmol / g or more, and even more preferably 0.70 mmol / g or more. This is because, within the above range, peeling of the electrode active material layer from the current collector is further suppressed. Furthermore, this is because, within the above range, polymerization stability during production of the electrode binder polymer is improved, allowing a high-quality electrode binder polymer to be obtained at low cost.

[0021] From the viewpoint of ensuring polymerization stability when producing the binder polymer, the content F1 of the first functional group in the electrode binder polymer of the present disclosure is preferably 5.0 mmol / g or less, more preferably 3.0 mmol / g or less, even more preferably 1.5 mmol / g or less, and particularly preferably 1.0 mmol / g or less.

[0022] The content F1 of the first functional group in the electrode binder polymer of the present disclosure may be 0.20 mmol / g to 5.0 mmol / g, 0.50 mmol / g to 3.0 mmol / g, 0.70 mmol / g to 1.5 mmol / g, or 0.70 mmol / g to 1.0 mmol / g.

[0023] The content F1 [mmol / g] of the first functional group is determined by the following method: Content F1 [mmol / g] of the first functional group = (content [mmol] of the first functional group) / (total weight [g] of the monomers used in producing the electrode binder polymer) In the formula, the "content [mmol] of the first functional group" is the sum of (amount of substance (mmol) of the monomer having the first functional group) x (the number of first functional groups per monomer having the first functional group) for all the monomers having the first functional group contained in the electrode binder polymer.

[0024] The content F2 of the second functional group in the electrode binder polymer of the present disclosure is preferably 0.020 mmol / g or more, more preferably 0.050 mmol / g or more, and even more preferably 0.070 mmol / g or more, because within the above range, the high-temperature storage properties of the electrode containing the electrode binder polymer are further improved.

[0025] The second functional group content F2 of the electrode binder polymer of the present disclosure is preferably 2.0 mmol / g or less, more preferably 1.0 mmol / g or less, even more preferably 0.60 mmol / g or less, and particularly preferably 0.10 mmol / g or less, because within the above ranges, the polymerization stability during production of the electrode binder polymer is improved, thereby improving the yield and enabling the production cost of the electrode binder polymer to be reduced.

[0026] The second functional group content F2 of the electrode binder polymer of the present disclosure may be 0.020 mmol / g to 2.0 mmol / g, 0.050 mmol / g to 1.0 mmol / g, 0.070 mmol / g to 0.60 mmol / g, or 0.070 mmol / g to 0.10 mmol / g.

[0027] The content F2 [mmol / g] of the second functional group is determined by the following method: Content F2 [mmol / g] of the second functional group = (content of the second functional group [mmol]) / (total weight [g] of the monomers used in producing the electrode binder polymer) In the formula, the "content of the second functional group" [mmol] is the total sum of (amount of substance (mmol) of the monomer having the second functional group) x (the number of second functional groups per monomer having the second functional group) for all the monomers having the second functional group contained in the electrode binder polymer.

[0028] In the electrode binder polymer of the present disclosure, from the viewpoint of improving the high-temperature storage characteristics of a battery using an electrode comprising the electrode binder polymer, the ratio F2 / F1 of the content F2 of the second functional group to the content F1 of the first functional group is preferably 0.020 or more, more preferably 0.050 or more, even more preferably 0.070 or more, and particularly preferably 0.082 or more. In the electrode binder polymer of the present disclosure, from the viewpoint of ensuring polymerization stability during production of the electrode binder polymer, the ratio F2 / F1 of the content F2 of the second functional group to the content F1 of the first functional group is preferably 2.0 or less, more preferably 1.0 or less, even more preferably 0.60 or less, and particularly preferably 0.10 or less.

[0029] In the electrode binder polymer of the present disclosure, the ratio F2 / F1 of the content F2 of the second functional group to the content F1 of the first functional group may be 0.020 to 2.0, 0.050 to 1.0, 0.082 to 0.60, or 0.082 to 0.10.

[0030] In the present disclosure, a carboxy group that forms a salt refers to a group in which a carboxy group forms a salt with a basic substance.

[0031] In the present disclosure, a blocked isocyanato group refers to a functional group formed by bonding an isocyanato group with a blocking agent. The blocked isocyanato group preferably has a structure that allows controllable conversion to an isocyanato group. The blocked isocyanato group preferably has a structure that generates an isocyanato group in response to an external stimulus, a chemical reaction, or the like, and more preferably has a structure that generates an isocyanato group in response to at least one selected from the group consisting of heating, voltage application, and chemical reaction. The conversion of a blocked isocyanato group to an isocyanato group can occur when the blocking agent is eliminated by a redox reaction, such as a reaction due to heating, a chemical reaction with a Lewis acid, a Bronsted acid, or the like, or an electrochemical reaction due to voltage application. Examples of blocking agents include methyl salicylate, 3,5-dimethylpyrazole, 2-butanone oxime (methyl ethyl ketoxime), ε-caprolactam, and 1-methoxy-2-propanol. The blocking agent preferably contains at least one selected from the group consisting of methyl salicylate, 3,5-dimethylpyrazole, and 2-butanone oxime, because it is easily removed.

[0032] The presence of the first functional group in the electrode binder polymer can be confirmed by quantifying the amount of carboxyl group or carboxylate salt present by infrared spectroscopy (IR), nuclear magnetic resonance (NMR), etc. Furthermore, the presence of the second functional group in the electrode binder polymer can be confirmed by quantifying the amount of blocking agent bonded to the isocyanato group or blocked isocyanato group present by infrared spectroscopy (IR), nuclear magnetic resonance (NMR), etc.

[0033] The glass transition point Tg of the electrode binder polymer of the present disclosure is -3°C or higher, preferably 0°C or higher, and more preferably 5°C or higher. The above ranges are intended to improve the film rupture strength of the electrode binder polymer and to suppress an increase in electrode resistance after an electrode containing the electrode binder polymer is placed in a high-temperature environment. From the viewpoint of ensuring the electrode peel strength of an electrode containing the electrode binder polymer, the glass transition point Tg of the electrode binder polymer of the present disclosure is preferably 50°C or lower, more preferably 30°C or lower, even more preferably 20°C or lower, and particularly preferably 10°C or lower. The glass transition point Tg of the electrode binder polymer of the present disclosure may be -3°C to 50°C, 0°C to 30°C, 5°C to 20°C, or 5°C to 10°C.

[0034] The glass transition point Tg of the binder polymer (P) is the peak top temperature of a chart obtained as a temperature derivative when measurement is performed using a differential scanning calorimetry (DSC) device (e.g., EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation) at a temperature rise rate of 10°C / min under a nitrogen gas atmosphere.

[0035] The electrode binder polymer of the present disclosure preferably has dispersibility in water. Having dispersibility in water means that the electrode binder polymer continues to exist in water without agglomeration or sedimentation. For example, this can be confirmed by visually confirming sedimentation, measuring the concentration gradient in the height direction in a container, and measuring the particle size by dynamic light scattering (DLS). The solubility of the electrode binder polymer in water at 25°C is 1.0 g / 100 gH ２ It is preferable that the density is 0 or less, and 0.50 g / 100 gH ２ It is more preferable that the density is 0 or less, and 0.30 g / 100 gH ２It is more preferable that the viscosity is 0 or less. When the viscosity is within the above range, an increase in viscosity can be suppressed when an electrode binder composition containing the electrode binder polymer of the present disclosure and an aqueous medium is prepared. Furthermore, when the viscosity is within the above range, the electrode binder polymer exists as particles in an electrode produced using the electrode binder composition containing the electrode binder polymer of the present disclosure. This makes it easier for the electrolyte solution to penetrate between the particles, and tends to reduce the electrode resistance.

[0036] <Structural Example of Electrode Binder Polymer> The electrode binder polymer of the present disclosure is not particularly limited in terms of its skeleton, as long as it has a first functional group and a second functional group. For example, the electrode binder polymer may have a structural unit having a first functional group and a structural unit having a second functional group. Hereinafter, the structural unit having the first functional group will also be referred to as a first structural unit, and the structural unit having the second functional group will also be referred to as a second structural unit.

[0037] The electrode binder polymer of the present disclosure may further include one or more other structural units that do not fall into either the first structural unit or the second structural unit, such as a third structural unit derived from an aromatic hydrocarbon monomer, a fourth structural unit derived from a nonionic monomer, or a fifth structural unit derived from a polyfunctional monomer.

[0038] Each monomer may have an ethylenically unsaturated bond. In the present disclosure, unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability. When each monomer has an ethylenically unsaturated bond, the structural units contained in the polymer are bonded to each other by a polymerization reaction of the ethylenically unsaturated bonds contained in each monomer. In this case, the structural units contained in the polymer are bonded to each other by a covalent bond, unless otherwise specified.

[0039] In addition, in the case of a polymer having a structural unit A derived from a compound A having an ethylenically unsaturated bond, the chemical structure of the portion of the structural unit A of the polymer other than the portion corresponding to the ethylenically unsaturated bond of the compound A is the same as the chemical structure of the portion other than the ethylenically unsaturated bond in the compound A before polymerization. For example, a structural unit derived from styrene is "-CH ２CH(C ６ H ５ It has the structure "(phenyl group))-".

[0040] When each monomer has an ethylenically unsaturated bond, the monomer from which a certain structural unit in a polymer is derived refers to a compound in which the bond between two carbon atoms forming the main chain of the polymer in that structural unit is replaced with an ethylenically unsaturated bond and separated from other structural units.

[0041] Furthermore, when a portion other than the main chain structure corresponding to the ethylenically unsaturated bond in a polymer, for example, the structure of a functional group such as a carboxy group, is changed by a chemical reaction or the like, the structural unit is classified based on the chemical structure after the change. For example, when vinyl acetate is polymerized and then saponified, this structural unit is referred to as a structural unit derived from vinyl alcohol, not as a structural unit derived from vinyl acetate. For example, when ion exchange is performed after polymerization of a monomer having an ionic functional group, the structural unit is classified based on the chemical structure after ion exchange. Specifically, for example, after polymerization of sodium acrylate, the corresponding structural unit is converted by ion exchange into "-CH ２ When the structural unit is expressed as "CH(COOH)-", this structural unit is referred to as a structural unit derived from acrylic acid, not as a structural unit derived from sodium acrylate.

[0042] [First structural unit] The first structural unit has at least one type selected from the group consisting of a carboxy group and a salt-forming carboxy group as a first functional group. The electrode binder polymer may contain one type of first structural unit alone or two or more types.

[0043] The first structural unit may have one carboxy group or two or more carboxy groups within one structural unit. The first structural unit may have one carboxy group that forms a salt within one structural unit, or two or more carboxy groups that form a salt within one structural unit. In the first structural unit, the total number of carboxy groups and carboxy groups that form a salt contained within one structural unit is preferably 1 to 4, and more preferably 1 to 2.

[0044] Examples of the carboxylic acid monomer from which the first structural unit is derived include unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid and fumaric acid. From the viewpoint of suppressing peeling of the electrode active material layer from the current collector, the carboxylic acid monomer preferably contains at least one selected from the group consisting of acrylic acid, methacrylic acid, and itaconic acid. The proportion of structural units derived from acrylic acid, methacrylic acid, and itaconic acid in the first structural unit (when two or more types are contained, the total proportion of structural units derived from these) is preferably 80 mol% or more, and may be 90 mol% or more, or may be 100 mol% or more.

[0045] Furthermore, from the viewpoint of improving the adhesion between the binder polymer and the active material or current collector, the carboxylic acid monomer may contain both an unsaturated monocarboxylic acid and an unsaturated dicarboxylic acid. When the carboxylic acid monomer contains both an unsaturated monocarboxylic acid and an unsaturated dicarboxylic acid, the content of the unsaturated dicarboxylic acid relative to the total amount of the unsaturated monocarboxylic acid and the unsaturated dicarboxylic acid is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, and particularly preferably 15 mol% or more. Furthermore, the content of the unsaturated dicarboxylic acid relative to the total amount of the unsaturated monocarboxylic acid and the unsaturated dicarboxylic acid is preferably 70 mol% or less, more preferably 50 mol% or less, even more preferably 40 mol% or less, and particularly preferably 30 mol% or less.

[0046] Examples of the salt include metal salts, ammonium salts, etc. Examples of the metal salt include alkali metal salts such as lithium salts, sodium salts, and potassium salts.

[0047] [Second structural unit] The second structural unit has at least one second functional group selected from the group consisting of an isocyanato group and a blocked isocyanato group. The electrode binder polymer may contain one type of second structural unit alone or two or more types.

[0048] Examples of the isocyanate monomer from which the second structural unit is derived include compounds having a (meth)acryloyl group, a vinyl group, or an allyl group. From the viewpoints of availability and polymerization reactivity, a compound having a (meth)acryloyl group is preferred. The isocyanate monomer is preferably a compound having a (meth)acryloyl group and at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group, and more preferably a (meth)acrylic acid ester having at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group. The proportion of structural units derived from a (meth)acrylic acid ester having at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group in the second structural unit is preferably 80 mol% or more, or may be 90 mol% or more, or may be 99 mol% or more.

[0049] The proportion of blocked isocyanato groups in the total amount of isocyanato groups and blocked isocyanato groups in the electrode binder polymer is preferably 50 mol % or more, may be 70 mol % or more, may be 90 mol % or more, or may be 100 mol %. Blocked isocyanato groups tend to suppress the conversion of isocyanato groups to amino groups by hydrolysis.

[0050] In the above, an example was described in which the first functional group and the second functional group are contained in separate structural units, but both the first functional group and the second functional group may be contained in a single structural unit.

[0051] [Third Structural Unit] The third structural unit is a structural unit derived from an aromatic hydrocarbon monomer. When an electrode binder polymer contains the third structural unit, the high-temperature storage characteristics of a battery using an electrode containing the electrode binder polymer tend to be improved. The electrode binder polymer may contain one type of third structural unit alone or two or more types. The electrode binder polymer may not contain the third structural unit. The aromatic hydrocarbon monomer preferably has an ethylenically unsaturated bond, is composed of a hydrocarbon, and does not contain atoms such as oxygen atoms. The third structural unit may have one aromatic ring or two or more aromatic rings within one structural unit. In the third structural unit, the number of aromatic rings contained within one structural unit is preferably 1 to 4, more preferably 1. The aromatic ring includes a benzene ring which may have a substituent. Examples of aromatic hydrocarbon monomers include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene.

[0052] [Fourth Structural Unit] The fourth structural unit is a structural unit derived from a nonionic monomer. When the electrode binder polymer has the fourth structural unit, the flexibility and electrode peel strength of an electrode containing the electrode binder polymer tend to be improved. The electrode binder polymer may contain one type of fourth structural unit alone or two or more types. The electrode binder polymer may not have the fourth structural unit. The nonionic monomer is preferably a nonionic (meth)acrylic acid ester having an ethylenically unsaturated bond and having neither an anionic functional group nor a cationic functional group. The nonionic monomer preferably contains a (meth)acrylic acid ester, more preferably a (meth)acrylic acid alkyl ester. The fourth structural unit may have a polar functional group. Examples of polar functional groups include, but are not limited to, a hydroxy group and a cyano group. Note that the hydroxy group as a polar functional group does not necessarily include an OH structure contained in an ionic functional group such as a carboxy group or a sulfo group (sulfonic acid group). Examples of the nonionic monomer having a polar functional group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile.

[0053] [Fifth Structural Unit] The fifth structural unit is a structural unit derived from a polyfunctional monomer. When the electrode binder polymer contains the fifth structural unit, the electrolyte resistance tends to be improved. The electrode binder polymer may contain one or more fifth structural units. The electrode binder polymer may not contain the fifth structural unit. The polyfunctional monomer is preferably a compound having multiple independent ethylenically unsaturated bonds. Here, multiple independent ethylenically unsaturated bonds refer to multiple ethylenically unsaturated bonds that do not form conjugated dienes. The fifth structural unit may have one or more remaining ethylenically unsaturated bonds within the structural unit. For example, in the case of a divinylbenzene polymer, the divinylbenzene-derived structural unit may have a structure without an ethylenically unsaturated bond (a structure in which both portions corresponding to the two ethylenically unsaturated bonds of divinylbenzene are incorporated into the polymer chain), or a structure with one ethylenically unsaturated bond (a structure in which only a portion corresponding to one of the ethylenically unsaturated bonds is incorporated into the polymer chain).

[0054] [Other Structural Units] The electrode binder polymer may have other structural units that do not fall under any of the structural units 1 to 5. Examples of compounds from which the other structural units are derived include, but are not limited to, compounds or salts thereof having one ethylenically unsaturated bond and having an anionic functional group other than a carboxyl group, such as a sulfo group or a phosphate group, surfactants having one ethylenically unsaturated bond (hereinafter sometimes referred to as "polymerizable surfactants"), and compounds having one ethylenically unsaturated bond and functioning as a silane coupling agent (hereinafter sometimes referred to as "polymerizable silane coupling agents").

[0055] [Content of each structural unit in the electrode binder polymer] The physical properties of the electrode binder polymer, such as the glass transition temperature Tg, may be adjusted by adjusting the contents of the first to fifth structural units in the electrode binder polymer. For example, the total content of the first structural unit, the second structural unit, the third structural unit, and the fourth structural unit (hereinafter, the "first structural unit, the second structural unit, the third structural unit, and the fourth structural unit" may also be referred to as the "first to fourth structural units") in the electrode binder polymer is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more. It may be 98% by mass or more, or even 100% by mass. The total content of the first to fourth structural units in the electrode binder polymer may be 99.5% by mass or less.

[0056] <Method for Producing Electrode Binder Polymer> The method for producing the electrode binder polymer is not particularly limited. For example, the electrode binder polymer can be synthesized by copolymerizing (polymerization step) a compound having a first functional group and an ethylenically unsaturated bond (hereinafter also referred to as a "first monomer") with a compound having a second functional group and an ethylenically unsaturated bond (hereinafter also referred to as a "second monomer"). Furthermore, the electrode binder polymer may be copolymerized with at least one monomer selected from the group consisting of a monomer for forming a third structural unit, a monomer for forming a fourth structural unit, a monomer for forming a fifth structural unit, and a monomer for forming other structural units.

[0057] An example of a method for copolymerizing each monomer is emulsion polymerization. A typical emulsion polymerization method in which monomers are emulsion-polymerized in an aqueous medium can be used as the emulsion polymerization method. The aqueous medium is preferably at least one selected from the group consisting of water and hydrophilic solvents. One hydrophilic solvent may be used alone, or two or more may be used in combination. Examples of hydrophilic solvents include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium is preferably water. A mixture of water and a hydrophilic solvent may also be used as the aqueous medium.

[0058] <Electrode Binder> The electrode binder of the present disclosure includes the electrode binder polymer of the present disclosure. The electrode binder of the present disclosure is preferably contained in an electrode of a nonaqueous secondary battery, more preferably in an electrode of a lithium ion secondary battery, and even more preferably in a negative electrode of a lithium ion secondary battery.

[0059] In the electrode binder, functional groups contained in the electrode binder polymer may react with other components, causing the structure of the electrode binder polymer to partially change. In this case, the structure of the electrode binder polymer after the reaction is also considered to be the electrode binder polymer. In other words, in the electrode binder, the electrode binder polymer includes the corresponding polymer and the structure of the polymer after it has reacted with other components.

[0060] The electrode binder may contain a polymer other than the electrode binder polymer, a surfactant, etc. The electrode binder is obtained by mixing these components.

[0061] The electrode binder preferably comprises the nonvolatile component in the electrode binder composition described below. The definition of the nonvolatile component in the electrode binder composition will be described later in the explanation of the electrode binder composition.

[0062] The content of the electrode binder polymer in the binder for a non-aqueous secondary battery is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 98% by mass or more, because the effect of including the electrode binder polymer becomes significant.

[0063] <Electrode binder composition> The electrode binder composition of the present disclosure includes the electrode binder polymer of the present disclosure and an aqueous medium. The electrode binder composition of the present disclosure is preferably used for producing an electrode for a non-aqueous secondary battery, more preferably for producing an electrode for a lithium ion secondary battery, and even more preferably for producing a negative electrode for a lithium ion secondary battery.

[0064] The electrode binder composition may be obtained by mixing the electrode binder polymer of the present disclosure with an aqueous medium, or may be obtained by mixing the electrode binder of the present disclosure with an aqueous medium.

[0065] In the electrode binder composition, functional groups or the like contained in the electrode binder polymer may react with other components, causing the structure of the electrode binder polymer to partially change. In this case, the structure of the electrode binder polymer after the reaction is also considered to be the electrode binder polymer. That is, in the electrode binder composition, the electrode binder polymer includes the corresponding polymer and the structure of the polymer after it has reacted with other components.

[0066] The electrode binder composition is preferably an emulsion in which particles containing an electrode binder polymer are dispersed in an aqueous medium. Examples of particles containing an electrode binder polymer include particles made of an electrode binder polymer, particles containing an electrode binder polymer and a surfactant, and particles containing other components. The electrode binder composition may also contain both particles containing an electrode binder polymer and particles not containing an electrode binder polymer.

[0067] The electrode binder composition may contain other components in addition to the electrode binder polymer and the aqueous medium. Specifically, the electrode binder composition may contain the components used in the synthesis of the electrode binder polymer.

[0068] The electrode binder composition of the present disclosure may be a dispersion obtained by emulsion polymerization of an ethylenically unsaturated compound. Alternatively, the electrode binder composition of the present disclosure may be a dispersion obtained by dispersing an electrode binder polymer obtained by a method other than emulsion polymerization in an aqueous medium.

[0069] The aqueous medium in the electrode binder composition of the present disclosure is preferably at least one selected from the group consisting of water and hydrophilic solvents. The hydrophilic solvents may be used alone or in combination of two or more. The aqueous medium preferably contains water, more preferably 50% by mass or more, even more preferably 70% by mass or more, and particularly preferably 90% by mass or more.

[0070] Examples of the hydrophilic solvent include the same hydrophilic solvents as those exemplified as the aqueous medium used in the synthesis of the electrode binder polymer. The aqueous medium may be the same as or different from the aqueous medium used in the synthesis of the electrode binder polymer.

[0071] From the viewpoint of increasing the amount of the active ingredient contained in the electrode binder composition, the nonvolatile content of the binder composition of the present disclosure is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. The nonvolatile content of the electrode binder composition can be adjusted by the content of the aqueous medium contained in the electrode binder composition.

[0072] The non-volatile content concentration of the electrode binder composition is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less, from the viewpoint of suppressing an increase in the viscosity of the electrode binder composition and facilitating the preparation of an electrode slurry, which will be described later.

[0073] The "non-volatile content" in the electrode binder composition is the component that remains as a solid or liquid after the composition is dried at 105°C for 1 hour in a dryer with circulating air at 1 atmosphere (1013 hPa). The form of the composition includes, but is not limited to, a solution, a dispersion, and a slurry.

[0074] The "non-volatile content concentration" in the binder composition is the mass ratio (mass %) of the mass of components remaining as a solid or liquid after weighing 1 g of the composition into an aluminum dish with a diameter of 5 cm and drying it for 1 hour at 105°C while circulating air in a dryer at 1 atmosphere (1013 hPa), relative to the mass (1 g) of the composition before drying.

[0075] <Electrode Slurry> The electrode slurry of the present disclosure includes the electrode binder polymer of the present disclosure, an aqueous medium, and an electrode active material. The electrode slurry of the present disclosure is preferably used for producing an electrode for a nonaqueous secondary battery, more preferably for producing an electrode for a lithium ion secondary battery, and even more preferably for producing a negative electrode for a lithium ion secondary battery.

[0076] The electrode slurry may be obtained by mixing the electrode binder polymer of the present disclosure, an electrode active material, and an aqueous medium, or may be obtained by mixing the electrode binder of the present disclosure, an electrode active material, and an aqueous medium, or may be obtained by mixing the electrode binder composition of the present disclosure and an electrode active material.

[0077] In the electrode slurry, functional groups and the like contained in the electrode binder polymer may react with other components, causing the structure of the electrode binder polymer to partially change. In this case, the structure of the electrode binder polymer after the reaction is also considered to be the electrode binder polymer. That is, in the electrode slurry, the electrode binder polymer includes the corresponding polymer and the structure of the polymer after it has reacted with other components.

[0078] The electrode binder polymer and the electrode active material contained in the electrode slurry are preferably dispersed in an aqueous medium. The electrode slurry may also contain a thickener, a conductive assistant, components used in the synthesis of the electrode binder polymer, and the like.

[0079] The content of the electrode binder polymer in the electrode slurry is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, relative to 100 parts by mass of the electrode active material. When the content of the electrode binder polymer is within the above range, the effect of including the electrode binder polymer tends to be more sufficiently exhibited.

[0080] The content of the electrode binder polymer in the electrode slurry is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, relative to 100 parts by mass of the electrode active material. When the content of the electrode binder polymer is within the above range, the content of the electrode active material in the electrode slurry can be increased, and the charge-discharge characteristics tend to be excellent.

[0081] The content of the electrode active material in the electrode slurry is preferably 80 parts by mass or more, and more preferably 90 parts by mass or more, per 100 parts by mass of the electrode slurry. When the content of the electrode active material is in the above range, the charge-discharge characteristics tend to be excellent.

[0082] The electrode active material contained in the electrode slurry is a material that allows intercalation and deintercalation of ions that serve as charge carriers, such as lithium ions. The ions that serve as charge carriers are preferably alkali metal ions, more preferably lithium ions, sodium ions, or potassium ions, and even more preferably lithium ions.

[0083] When the electrode produced using the electrode slurry is a negative electrode, the electrode active material is a negative electrode active material. The negative electrode active material preferably includes at least one selected from the group consisting of a carbon material, a silicon-containing material, and a titanium-containing material. These materials used as the negative electrode active material may be used alone, in combination with two or more, or in a composite.

[0084] Examples of carbon materials used as negative electrode active materials include cokes such as petroleum coke, pitch coke, and coal coke, carbonized organic polymers, and graphites such as artificial graphite and natural graphite. Examples of silicon-containing materials used as negative electrode active materials include elemental silicon and silicon compounds such as silicon oxide. Examples of titanium-containing materials used as negative electrode active materials include lithium titanate.

[0085] The negative electrode active material preferably contains at least one selected from the group consisting of a carbon material and a silicon-containing material. When the negative electrode active material is such a material, the effect of the electrode binder polymer contained in the electrode slurry to improve the binding between the negative electrode active materials and between the negative electrode active material and the current collector tends to be greater.

[0086] When the electrode produced using the electrode slurry is a positive electrode, the electrode active material is a positive electrode active material. As the positive electrode active material, a material having a more noble standard electrode potential than the negative electrode active material is used. Specifically, as the positive electrode active material, lithium composite oxides containing nickel, such as Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides, lithium cobalt oxide (LiCoO ２ ), spinel-type lithium manganese oxide (LiMn２ O ４ ), olivine-type lithium iron phosphate, TiS ２ , MnO ２ , MoO ３ , V ２ O ５ These substances used as the positive electrode active material may be used alone or in combination of two or more.

[0087] The aqueous medium contained in the electrode slurry of the present disclosure is preferably one selected from the group consisting of water and hydrophilic solvents. Examples of the hydrophilic solvent include the same hydrophilic solvents as those exemplified as the aqueous medium used in the synthesis of the electrode binder polymer. The aqueous medium contained in the electrode slurry may be the same as or different from the aqueous medium used in the synthesis of the electrode binder polymer.

[0088] Examples of thickeners that can be contained in the electrode slurry include cellulose derivatives such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose, and hydroxypropyl cellulose, ammonium salts of cellulose derivatives, alkali metal salts of cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, poly(meth)acrylates, poly(meth)acrylamide, and poly(meth)N-hydroxyalkylacrylamide. From the viewpoint of dispersibility of the electrode active material in the electrode slurry, the thickener preferably contains at least one selected from the group consisting of carboxymethyl cellulose, ammonium salts of carboxymethyl cellulose, and alkali metal salts of carboxymethyl cellulose.

[0089] When the electrode slurry contains a thickener, the content of the thickener in the electrode slurry is preferably 0.50 parts by mass or more, and more preferably 0.80 parts by mass or more, relative to 100 parts by mass of the electrode active material. When the content of the thickener is within the above range, the coatability of the electrode slurry tends to be good.

[0090] The content of the thickener in the electrode slurry is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, relative to 100 parts by mass of the electrode active material, which tends to improve the binding between the electrode active materials contained in the electrode produced using the electrode slurry and between the electrode active material and the current collector.

[0091] Examples of conductive additives that can be contained in the electrode slurry include carbon black and carbon fiber. Examples of carbon black include furnace black, acetylene black, Denka Black (manufactured by Denka Co., Ltd.), and Ketjen Black (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fiber include carbon nanotubes and carbon nanofibers. Examples of carbon nanotubes include VGCF (manufactured by Resonac Co., Ltd.), which is a vapor-grown carbon fiber.

[0092] The electrode slurry of the present disclosure can be produced, for example, by mixing the electrode binder polymer of the present disclosure, an electrode active material, an aqueous medium, a thickener that is optionally contained, a conductive aid that is optionally contained, and other components that are optionally contained. The order of mixing the components that are the raw materials of the electrode slurry is not particularly limited and can be determined as appropriate. Examples of methods for mixing the components include methods using a mixing device such as a stirring type, a rotary type, or a shaking type.

[0093] <Electrode> The electrode of the present disclosure has a current collector and an electrode active material layer containing an electrode active material and the electrode binder polymer of the present disclosure. The shape of the electrode is not particularly limited, and may be a laminate, a wound body, or the like. The electrode of the present disclosure is preferably an electrode for a nonaqueous secondary battery, more preferably an electrode for a lithium ion secondary battery, and even more preferably a negative electrode for a lithium ion secondary battery.

[0094] In addition, functional groups contained in the electrode binder polymer may react in the electrode, causing the structure of the electrode binder polymer to partially change. In this case, the structure of the electrode binder polymer after the reaction is also considered to be the electrode binder polymer. That is, in the electrode, the electrode binder polymer includes the corresponding polymer and the structure of the polymer after the reaction and change.

[0095] The area on the current collector where the electrode active material layer is formed is not particularly limited, and the electrode active material layer may be formed on the entire surface of the current collector, or may be formed on only a part of the surface of the current collector. When the current collector is in the shape of a plate, foil, or the like, the electrode active material layer may be formed on both surfaces of the current collector, or may be formed on only one surface.

[0096] The current collector is preferably a metal sheet. Examples of metals forming the metal sheet include iron, copper, aluminum, nickel, and stainless steel. When the electrode of the present disclosure is a negative electrode of a lithium-ion secondary battery, the current collector is preferably a copper foil. The thickness of the metal sheet is not particularly limited, and is preferably 0.001 mm to 0.5 mm.

[0097] The electrode active material layer includes an electrode active material and the electrode binder polymer of the present disclosure. The electrode active material layer may also include a conductive aid, a thickener, etc. The electrode active material, the conductive aid, and the thickener may all be the same as those exemplified as components of the electrode slurry.

[0098] The electrode of the present disclosure can be manufactured, for example, by the method described below. First, the electrode slurry of the present disclosure is applied to at least a portion of the surface of a current collector. Next, the electrode slurry is dried to obtain an electrode sheet in which an electrode active material layer is formed on the current collector. Thereafter, if necessary, the electrode sheet is cut to a size and shape appropriate for the size and shape of the battery to obtain an electrode. Note that if cutting is not necessary, the electrode sheet may be used as an electrode as is.

[0099] The method for applying the electrode slurry to the current collector is not particularly limited, and examples thereof include a reverse roll method, a direct roll method, a doctor blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, a dip method, and a squeeze method. Among these application methods, in consideration of the physical properties such as viscosity of the electrode slurry and drying properties, it is preferable to use at least one method selected from the group consisting of a direct roll method, a doctor blade method, a knife method, and an extrusion method. When these methods are applied, an electrode active material layer having a smooth surface and small thickness variation tends to be obtained.

[0100] The area on the current collector to which the electrode slurry is applied is not particularly limited, and may be the entire surface of the current collector or only a part of the surface of the current collector. When the current collector is in the shape of a plate, foil, or the like, the electrode slurry may be applied to both surfaces or only one surface of the current collector.

[0101] When the electrode slurry is applied to both sides of the current collector, it may be applied to each side sequentially or simultaneously. The electrode slurry may be applied to the current collector continuously or intermittently. The amount of electrode slurry to be applied can be determined appropriately depending on the design capacity of the battery, the composition of the electrode slurry, and the like.

[0102] The method for drying the electrode slurry applied to the current collector is not particularly limited, and for example, hot air drying, reduced pressure drying, vacuum drying, (far) infrared drying, low temperature air drying, or a combination thereof can be used.

[0103] The drying temperature and drying time when drying the electrode slurry can be appropriately adjusted depending on the nonvolatile content concentration in the electrode slurry, the amount of the electrode slurry applied to the current collector, etc. The drying temperature is preferably 40°C to 350°C, and from the viewpoint of productivity, more preferably 60°C to 100°C. The drying time is preferably 1 minute to 30 minutes.

[0104] The electrode sheet in which the electrode active material layer is formed on the current collector may be cut to a size and shape appropriate for the electrode. The method for cutting the electrode sheet is not particularly limited, and slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like may be used.

[0105] In the present disclosure, the electrode sheet may be pressed as needed before or after cutting, which allows the electrode active material to be more firmly bound to the current collector and also reduces the thickness of the electrode, thereby enabling the nonaqueous secondary battery to be made smaller.

[0106] A general method can be used to press the electrode sheet. It is particularly preferable to use a mold pressing method or a roll pressing method. When using a mold pressing method, the pressing pressure is not particularly limited, and is preferably 0.5 t / cm. ２ ~5t / cm ２ It is preferable to set the following.

[0107] When the roll press method is used, the press load is not particularly limited, but is preferably 0.5 t / cm to 10 t / cm. When the press load is in this range, the above-mentioned effects of pressing can be easily obtained, and a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into and from the electrode active material tends to be suppressed.

[0108] <Secondary Battery> The secondary battery of the present disclosure includes the electrode of the present disclosure. The secondary battery of the present disclosure is preferably a non-aqueous secondary battery, and more preferably a lithium-ion secondary battery. Below, a lithium-ion secondary battery will be described as a preferred example of the secondary battery of the present disclosure. Note that the configuration of the secondary battery of the present disclosure is not limited to the example shown below.

[0109] An example of a lithium ion secondary battery has a configuration in which a positive electrode, a negative electrode, and an electrolyte are housed in an exterior body. In addition to the above configuration, the lithium ion secondary battery may include, for example, a separator between the positive electrode and the negative electrode, or may include other components. The shape of the lithium ion secondary battery may be any shape, such as a coin type, a button type, a sheet type, a cylindrical type, a prismatic type, or a flat type.

[0110] In one example of a lithium-ion secondary battery according to the present disclosure, one or both of a positive electrode and a negative electrode contain the electrode binder polymer according to the present disclosure. The electrode binder polymer is preferably contained in an electrode active material layer of the electrode. It is preferable that at least one of the positive electrode active material layer and the negative electrode active material layer contains the electrode binder polymer, and it is more preferable that the negative electrode active material layer contains the electrode binder polymer.

[0111] In a lithium ion secondary battery according to an example of the present disclosure, when only one of the positive electrode active material layer and the negative electrode active material layer contains the electrode binder polymer according to the present disclosure, the other electrode active material layer contains polyvinylidene fluoride or the like as a binder.

[0112] The electrolyte solution is preferably a non-aqueous liquid having ion conductivity, such as a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, or the like, and the former is preferred from the viewpoint of obtaining a lithium ion secondary battery with low production cost and low internal resistance.

[0113] The electrolyte can be an alkali metal salt, and can be appropriately selected depending on the type of electrode active material, etc. The electrolyte can be LiClO ４ , LiBF ６ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiB １０ Cl １０ , LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ , C.F. ３ SO ３ Li, C.H. ３ SO ３ Li, LiCF ３ SO ３ , LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ２Examples of the electrolyte include lithium carboxylate, lithium cations of N, and aliphatic carboxylates. Other alkali metal salts can also be used as the electrolyte.

[0114] The organic solvent for dissolving the electrolyte is not particularly limited, and examples thereof include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC), and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The organic solvent may be used alone or in combination of two or more. Among these, it is preferable to use two or more linear carbonate solvents in combination as the organic solvent.

[0115] The electrolyte may contain additives in addition to the above components. Examples of additives include nitrile compounds, sulfur-containing compounds, and boron-containing compounds. Examples of nitrile compounds include succinonitrile and acetonitrile. Examples of sulfur-containing compounds include compounds having a sulfonyl group, a sulfonate group, or a sultone structure, such as methyl ethyl sulfone and 1,3-propane sultone. Examples of boron-containing compounds include boric acid esters.

[0116] The exterior body may be made of an aluminum laminate material made of aluminum foil and a resin film, but is not limited to this.

[0117] Hereinafter, one example of the embodiment of the present disclosure will be specifically described using examples, but the embodiment is not limited to these examples.

[0118] In the following examples, a negative electrode of a lithium ion secondary battery was fabricated as an example of an electrode according to the present disclosure, and a lithium ion secondary battery was fabricated as an example of a secondary battery, and the negative electrode and the lithium ion secondary battery were compared with those of comparative examples. Furthermore, the water used in the following examples and comparative examples is ion-exchanged water unless otherwise specified.

[0119] <Production of electrode binder polymer and electrode binder composition> In each example and comparative example, the amounts (parts by mass) of the respective monomers shown in Table 1 were mixed to prepare emulsions.

[0120] Next, an aqueous solution was prepared by dissolving each of the polymerization initiators in the amounts (parts by mass) shown in Table 1 in 50 parts by mass of water.

[0121] A separable flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel was charged with 150 parts by mass of water, and the temperature was raised to 80° C. The monomer emulsion and the aqueous solution in which the polymerization initiator was dissolved were each continuously fed to the separable flask over a period of 3 hours while being stirred at 80° C., thereby carrying out emulsion polymerization, thereby obtaining emulsions containing particles containing the electrode binder polymer of Examples 1 to 6 and Comparative Examples 1 to 3 and an aqueous medium.

[0122] The obtained emulsion was cooled to room temperature (25°C). Then, 133 parts by mass of water and 25% by mass of aqueous ammonia were added. In this manner, the electrode binder compositions of Examples 1 to 6 and Comparative Examples 1 to 3 were produced, which were emulsions in which particles containing the electrode binder polymers of Examples 1 to 6 and Comparative Examples 1 to 3 were dispersed in an aqueous medium.

[0123]

[0124] The abbreviations for the monomers in Table 1 represent the following: AA: acrylic acid IA: itaconic acid St: styrene 2-EHA: 2-ethylhexyl acrylate BzMA: benzyl methacrylate 2-HEMA: 2-hydroxyethyl methacrylate DVB: divinylbenzene p-StSANa: sodium p-styrenesulfonate KH-10: polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt (Aqualon KH-10, polymerizable surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

[0125] As the monomer 2, a compound having a methacryloyloxy group and a blocked isocyanate group was used. Specifically, they are as follows: MOI-SM: 2-[[[[2-[(2-methyl-1-oxo-2-propen-1-yl)oxy]ethyl]amino]carbonyl]oxy]-methyl benzoate (Karenz MOI-SM (manufactured by Resonac Co., Ltd.)) MOI-BP: 2-[(3,5-dimethylpyrazolyl)carbonylamino]ethyl methacrylate (Karenz MOI-BP (manufactured by Resonac Co., Ltd.)) MOI-BM: 2-[0-(1'-methylpropylideneamino)carboxyamino]ethyl methacrylate (Karenz MOI-BM (manufactured by Resonac Co., Ltd.))

[0126] Rongalit SFS in the polymerization initiator is the trade name of Rongalit manufactured by Sumitomo Seika Chemicals Co., Ltd. The amount of ammonia as a basic substance shown in Table 1 is the amount (parts by mass) of ammonia contained in ammonia water. The amount of water as an aqueous medium shown in Table 1 is the total amount (parts by mass) of water contained in the electrode binder composition.

[0127] The content F1 of the first functional group and the content F2 of the second functional group in the electrode binder polymer were determined by the above-mentioned method.

[0128] [Measurement of Glass Transition Temperature Tg] Each of the electrode binder compositions of Examples 1 to 6 or Comparative Examples 1 to 3 was applied onto a release PET (polyethylene terephthalate) film and dried at 50°C for 5 hours to obtain a film having a thickness of 2 mm.

[0129] A square test piece measuring 2 mm in length and 2 mm in width was cut out from the obtained film. The test piece was sealed in an aluminum pan, and differential scanning calorimetry (DSC) measurement of the test piece was performed using a differential scanning calorimeter (EXSTAR DSC / SS7020, manufactured by Hitachi High-Tech Science Corporation) in a nitrogen gas atmosphere at a heating rate of 10°C / min. The temperature range for DSC measurement was -40°C to 200°C. The peak top temperature of the DSC chart obtained as the temperature derivative of the DSC was then measured, and this temperature was defined as the glass transition temperature Tg (°C) of the electrode binder polymer.

[0130] <Evaluation of Electrode Binder> [Measurement of Film Breaking Strength] The electrode binder composition prepared in each Example and Comparative Example was applied to a glass plate covered with a polypropylene sheet, and the applied film was measured at 23°C under atmospheric pressure and an absolute humidity of 10 g / m ３ The film was dried at 110°C under atmospheric pressure and an absolute humidity of 10 g / m for 5 days, and then dried under reduced pressure of 0.01 MPa or less at 60°C for 12 hours to form a film with a thickness of 0.4 mm. The formed film was peeled off from the polypropylene sheet to prepare the following film (I) or (II): (I) Film to be used for measurement as is after peeling from the polypropylene sheet; (II) Film to be used for measurement as is after peeling from the polypropylene sheet at 110°C under atmospheric pressure and an absolute humidity of 10 g / m ３ Each of the films obtained in (I) and (II) was punched out to a length of 60 mm and a width of 10 mm to prepare a test piece. The atmospheric pressure was 1013 hPa.

[0131] A tensile test was performed on each test piece using a precision universal testing machine, Autograph AG-20kNX, manufactured by Shimadzu Corporation, to measure the film rupture strength [MPa]. The tensile direction was the longitudinal direction of the test piece. The chuck positions were set at two locations, 5 mm on both sides from the center in the longitudinal direction (positions 30 mm from both sides parallel to the width direction). In other words, the distance between the chucks was set to 10 mm. The tensile speed, i.e., the test speed, was set to 100 mm / min. The tensile test was performed at atmospheric pressure, 23°C, and an absolute humidity of 10 g / m ３ (relative humidity 50% RH).

[0132] The maximum load detected in the above test was divided by the cross-sectional area of ​​the test piece, 10 mm × 0.4 mm, to determine the film rupture strength of the electrode binder. The values ​​are shown in Table 2 as (I) film rupture strength S(23) [MPa] in the as-is state after film formation, and (II) film rupture strength S(110) [MPa] after standing at 110°C.

[0133] <Production of Lithium-Ion Secondary Battery> Negative electrodes were produced by the method described below using the electrode binder compositions of Examples 1 to 6 and Comparative Examples 1 to 3, respectively, and the lithium-ion secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 were produced using these negative electrodes.

[0134] (Preparation of Positive Electrode) LiNi as Positive Electrode Active Material０．６ Mn ０．２ Co ０．２ O ２ 94 parts by mass of the above, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to obtain a mixture, and 50 parts by mass of N-methylpyrrolidone was added to the obtained mixture and further mixed to obtain a positive electrode slurry.

[0135] A 15 μm thick aluminum foil was prepared as a positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector by a direct roll coating method. The amount of the positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described below was 125 μm per side.

[0136] The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes and pressed by a roll press (manufactured by Thank Metal Co., Ltd., press load 5 t / cm, roll width 7 cm) to obtain a positive electrode sheet having positive electrode active material layers on both sides of the positive electrode current collector. The obtained positive electrode sheet was cut into a rectangle 50 mm long and 40 mm wide, and a conductive tab was attached to form a positive electrode.

[0137] (Preparation of negative electrode) 96.9 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zishen Technology Co., Ltd.) as a negative electrode active material, 3.6 parts by mass of any of the electrode binder compositions produced in Examples 1 to 6 and Comparative Examples 1 to 3 (non-volatile content (binder polymer) 1.4 parts by mass), and 60 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethyl cellulose-sodium salt, manufactured by Nippon Paper Chemicals Co., Ltd., Sunrose MAC500LC) were mixed, and 16 parts by mass of water was added, and the mixture was mixed using a planetary centrifugal mixer (ARE-310, manufactured by Thinky Corporation) to obtain a negative electrode slurry (electrode slurry).

[0138] A copper foil having a thickness of 10 μm was prepared as a negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector by a direct roll method. The amount of the negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after the roll press treatment described below was 170 μm per side.

[0139] The negative electrode slurry applied to the negative electrode current collector was dried at 90°C for 10 minutes, and then pressed by a roll press using a roll press (manufactured by Thank Metal Co., Ltd., press load 8 t / cm, roll width 7 cm) to obtain a negative electrode sheet having a negative electrode active material layer on both sides of the negative electrode current collector. The obtained negative electrode sheet was cut into a rectangle 52 mm long and 42 mm wide, and a conductive tab was attached to form a negative electrode.

[0140] (Fabrication of Lithium-Ion Secondary Battery) A separator (made of polyethylene, 25 μm thick) made of a polyolefin-based porous film was interposed between the positive electrode and the negative electrode, and the positive electrode active material layer and the negative electrode active material layer were laminated so as to face each other, and the battery was housed in an exterior body (battery pack) made of an aluminum laminate material. Thereafter, an electrolyte solution was poured into the exterior body, vacuum impregnation was performed, and the battery was packed with a vacuum heat sealer to obtain a lithium-ion secondary battery.

[0141] The electrolyte solution was a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 30:50:20, and LiPF 5 at a concentration of 1.0 mol / L. ６ A mixture of 99 parts by mass of a solution in which the above was dissolved and 1 part by mass of vinylene carbonate was used.

[0142] <Evaluation of Nonaqueous Secondary Batteries> The lithium ion secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated by the following methods for the discharge capacity retention rate after 500 cycles, the discharge capacity retention rate after storage at 60° C. for 4 weeks, and the rate of increase in internal resistance (DCR) after storage at 60° C. for 4 weeks. The results are shown in Table 2.

[0143] [Discharge Capacity Retention Rate After 500 Cycles] Charge and discharge were performed under the condition of 45°C, with one cycle consisting of a series of operations of the following steps (i) to (iv). The time-integrated value of the current in steps (i) and (ii) was taken as the charge capacity, and the time-integrated value of the current in step (iv) was taken as the discharge capacity. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were measured, and the discharge capacity retention rate after 500 cycles was calculated using the following formula: Discharge capacity retention rate after 500 cycles (%) = 100 × (discharge capacity at the 500th cycle / discharge capacity at the first cycle)

[0144] (i) Charge at a current of 1 C until the voltage reaches 4.2 V (constant current (CC) charging). (ii) Charge at a voltage of 4.2 V until the current reaches 0.05 C (constant voltage (CV) charging). (iii) Leave to stand for 30 minutes. (iv) Discharge at a current of 1 C until the voltage reaches 2.75 V (constant current (CC) discharging).

[0145] [Discharge Capacity Retention Rate After 4 Weeks of Storage at 60°C] CC charging was performed at a current of 1C at 25°C until the voltage reached 4.2V, followed by CV charging until the current reached 0.05C. CC discharging was then performed at a current of 1C until the voltage reached 2.75V, and the resulting discharge capacity was recorded as the discharge capacity before storage. CC charging was then performed again at a current of 1C until the voltage reached 4.2V, followed by CV charging until the current reached 0.05C to obtain a fully charged battery. The resulting fully charged battery was left standing at 60°C for 4 weeks. CC discharging was then performed again at a current of 1C until the voltage reached 2.75V at 25°C, and the resulting discharge capacity was recorded as the discharge capacity after storage. The discharge capacity retention rate after 4 weeks of storage at 60°C was calculated from the discharge capacity before storage and the discharge capacity after storage using the following formula: Discharge capacity retention rate (%) after 4 weeks of storage at 60°C = 100 × (discharge capacity after storage / discharge capacity before storage).

[0146] [Rate of increase in internal resistance (DCR) after storage at 60°C for 4 weeks] The internal resistance (DCR (Ω)) of a lithium-ion secondary battery was measured under the condition of 25°C according to the following procedure. That is, the battery was charged and discharged at a constant current of 0.2 C from the rest potential until the voltage reached 3.6 V, and the state of charge was set to 50% of the initial capacity (SOC 50%). Then, the battery was discharged for 60 seconds at current values ​​of 0.2 C, 0.5 C, 1 C, and 2 C. After each discharge, the battery was charged to return to an SOC of 50%. The internal resistance DCR (Ω) at an SOC of 50% was determined from the relationship between these four current values ​​(values ​​for 1 second) and voltage.

[0147] The internal resistance (DCR) obtained by the above procedure was measured at the following stages (1) and (2): (1) Before storing for 4 weeks under the condition of being fully charged and at 60°C; (2) After storing for 4 weeks under the condition of being fully charged and at 60°C. The internal resistance (DCR) measured in (1) was defined as the DCR before storage, and the internal resistance (DCR) measured in (2) was defined as the DCR after storage. The rate of increase in internal resistance (DCR) after 4 weeks of storage at 60°C was calculated using the following formula: Rate of increase in internal resistance (DCR) after 4 weeks of storage at 60°C (%) = 100 × (DCR after storage / DCR before storage).

[0148]

[0149] <Evaluation Results> The electrode binder polymers synthesized in Examples 1 to 6 have a first functional group that is at least one selected from the group consisting of a carboxy group and a carboxy group that forms a salt, and a second functional group that is at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group, and have a glass transition temperature Tg of −3° C. or higher. Furthermore, all of the lithium ion secondary batteries produced using the electrode binder polymers synthesized in Examples 1 to 6 maintained a sufficient discharge capacity retention rate and showed only a small increase in DCR even after storage at 60° C. for 4 weeks.

[0150] The lithium ion secondary battery of Comparative Example 1, which was produced using an electrode binder polymer having no second functional group, showed a decrease in discharge capacity retention rate and a large increase in DCR after storage for 4 weeks at 60° C. The lithium ion secondary batteries of Comparative Examples 2 and 3, which were produced using an electrode binder polymer having a low glass transition temperature Tg, showed a decrease in discharge capacity retention rate after storage for 4 weeks at 60° C., although not as great as Comparative Example 1, and a large increase in DCR after storage for 4 weeks at 60° C.

[0151] From the above results, it can be said that a secondary battery with excellent high-temperature storage stability can be obtained by using an electrode binder polymer that has a first functional group that is at least one type selected from the group consisting of a carboxy group and a carboxy group that forms a salt, and a second functional group that is at least one type selected from the group consisting of an isocyanato group and a blocked isocyanato group, and that has a glass transition temperature Tg of −3° C. or higher.

[0152] Furthermore, the lithium ion secondary batteries of Examples 1 to 6 maintained a higher discharge capacity retention rate after 500 cycles than the lithium ion secondary batteries of Comparative Examples 1 to 3.

[0153] It is also clear that the films produced using the electrode binder polymers synthesized in Examples 1 to 6 have dramatically improved film rupture strength compared to the films produced using the electrode binder polymers synthesized in Comparative Examples 2 and 3. The electrode binder polymers synthesized in Examples 1 to 6 have higher glass transition temperatures Tg than the electrode binder polymers synthesized in Comparative Examples 2 and 3.

[0154] From this, it is thought that the breaking strength of a film produced using an electrode binder polymer varies greatly depending on the glass transition point Tg of the electrode binder polymer, and is particularly greatly affected by whether the glass transition point Tg is −3° C. or higher.

[0155] Therefore, it can be said that an electrode binder polymer having a first functional group that is at least one selected from the group consisting of a carboxy group and a carboxy group that forms a salt, and a second functional group that is at least one selected from the group consisting of an isocyanato group and a blocked isocyanato group, and having a glass transition temperature Tg of -3°C or higher, can provide a coating with high breaking strength. As a result, it is thought that an increase in DCR after storage of an electrode containing the electrode binder polymer at 60°C for 4 weeks is suppressed. Furthermore, by using an electrode binder polymer that can form a coating with high breaking strength, it can be expected that the strength of the electrode can be improved.

[0156] The disclosures of Japanese Patent Application Nos. 2023-214286, 2024-188626, and 2024-188627 are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An electrode binder polymer having a first functional group which is at least one type selected from the group consisting of a carboxy group and a carboxy group which forms a salt, and a second functional group which is at least one type selected from the group consisting of an isocyanato group and a blocked isocyanato group, and having a glass transition point Tg of -3°C or higher.

2. The electrode binder polymer according to claim 1, which has a glass transition point Tg of 50° C. or lower.

3. The electrode binder polymer according to claim 1, wherein the content F1 of the first functional group is 0.20 mmol / g to 5.0 mmol / g.

4. The electrode binder polymer according to claim 1, wherein the content F2 of the second functional group is 0.020 mmol / g to 2.0 mmol / g.

5. The electrode binder polymer according to claim 1, wherein the ratio F2 / F1 of the content F2 of the second functional group to the content F1 of the first functional group is 0.020 to 2.

0.

6. The electrode binder polymer according to claim 1, which has dispersibility in water.

7. An electrode binder comprising the electrode binder polymer according to any one of claims 1 to 6.

8. An electrode binder composition comprising the electrode binder polymer according to any one of claims 1 to 6 and an aqueous medium.

9. An electrode slurry comprising the electrode binder polymer according to any one of claims 1 to 6, an aqueous medium, and an electrode active material.

10. An electrode comprising: a current collector; and an electrode active material layer comprising an electrode active material and the electrode binder polymer according to any one of claims 1 to 6.

11. A secondary battery comprising the electrode according to claim 10.

12. A method for producing an electrode binder polymer according to any one of claims 1 to 6, comprising copolymerizing a compound having the first functional group and an ethylenically unsaturated bond with a compound having the second functional group and an ethylenically unsaturated bond.

13. A method for producing an electrode binder, comprising mixing the electrode binder polymer according to any one of claims 1 to 6.

14. A method for producing an electrode binder composition, comprising mixing the electrode binder polymer according to any one of claims 1 to 6 with an aqueous medium.

15. A method for producing an electrode binder composition, comprising mixing the electrode binder according to claim 7 with an aqueous medium.

16. A method for producing an electrode slurry, comprising mixing the electrode binder polymer according to any one of claims 1 to 6, an electrode active material, and an aqueous medium.

17. A method for producing an electrode slurry, comprising mixing the electrode binder according to claim 7, an electrode active material, and an aqueous medium.

18. A method for producing an electrode slurry, comprising mixing the electrode binder composition according to claim 8 with an electrode active material.

19. A method for producing an electrode, comprising applying the electrode slurry according to claim 9 to at least a portion of the surface of a current collector and drying the applied slurry.

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